(a) Field of the Invention
The present invention relates to a fin-type heat exchanger, and more particularly, to a fin-type heat exchanger in which an arrangement of slits formed on fins is improved to enhance heat exchange efficiency and reduce noise.
(b) Description of the Prior Art
Fin-type heat exchangers are generally structured to include a pipe bent a plurality of times, and fins disposed parallel to one another at predetermined intervals with the pipe passing therethrough. Such a heat exchanger is used in air conditioners, etc. to carry out heat exchange between external air passing over the fins and an external surface of the pipe, and operating fluid flowing through the pipe.
The fins receive heat from the pipe and exchange heat with the surrounding air. That is, heat from the pipe is transmitted to the fins such that an area of heat transmission is greatly increased. To further improve this function, a plurality of slits are formed by partially cutting out portions of the fin and bending the cut-outs so that they protrude from a surface of each fin. The slits are formed in groups around locations where the pipe passes through the fins so that air passes over the surface of the same after being directed onto the pipe.
Referring to FIGS. 4 and 5, shown respectively are a side view of a prior art fin 2 and a view taken along line V--V of FIG. 4. As shown in the drawings, a plurality of pipe holes 3a and 3b are formed in the fin 2, a pipe (not shown) passing through the pipe holes 3a and 3b. Formed in a longitudinal direction on a surface of the fin 2 and between the pipe holes 3a and 3b are a plurality of slits 4 and 5. That is, the slits 4 and 5 are formed in a direction perpendicular to a direction in which air passes between the fin 2 (shown by the arrows to the left of the fin 2 in the drawing).
In air conditioners, air is typically directed to the heat exchanger by a fan (not shown) to facilitate heat exchange. Here, the pipe holes 3a are positioned in a row on an upstream side of the fin 2 to form a first row 2a, while the pipe holes 3b are positioned in a row on a downstream side of the fin 2 to form a second row 2b. To improve heat-exchange efficiency (i.e. to expose as much of the outside surfaces of the pipe and fin 2 to the fan-blown air), the pipe holes 3a of the first row 2a are non-aligned with respect to the pipe holes 3b of the second row 2b in the direction of air flow.
Groups of slits 4 and 5, formed between the pipe holes 3a and 3b, respectively are formed by partially cutting-out portions of the fin and then bending the cut-outs such that they project from a fin surface. In the prior art fin of FIGS. 4-5, the cut-outs project from the same surface of the fin 2 and are formed in a plurality of rows. Further, the slits 4 formed between the pipe holes 3a of the first row 2a are identical in shape and pattern to the slits 5 formed between the pipe holes 3b of the second row 2b. The slits 4 and 5 act to improve heat transmission efficiency by minimizing the depth that can be achieved by the temperature boundary layer of the air flow.
However, in the above prior art fin-type heat exchanger, because the depth of the temperature boundary layer increases in a downstream direction of air flow, the heat transmission efficiency is decreased in that direction. Also, a formation of the slits 4 and 5 over substantially the entire surface of the fin 2 creates resistance to air flowing over the same such that heat transmission efficiency is reduced.
To remedy this problem, Japanese Laid-open Patent No. 4-93595 proposes a heat exchanger having a fin 12 as shown in FIGS. 6 and 7, respectively illustrating a side view of the fin 12 and a view taken along line VII--VII of FIG. 6.
As shown in the drawings, pipe holes 13a positioned in an upstream side of the fin 12 are non-aligned with respect to pipe holes 13b positioned in a downstream a side of the fin 12, as in the above-described prior art heat exchanger to improve heat-exchange efficiency.
Further, a groups of slits 14 and 15 are provided, respectively, between the pipe holes 13a and 13b on a surface of the fin 12, the slits 14 and 15 being formed in a plurality of rows 12a, 12b. However, the number of slits 14 formed in each group of the first row 12a is greater than the number of slits 15 formed in each group of the second row 12b. In addition, the slits 14 have their cut-outs projecting from both surfaces of the fin (see FIG. 7), whereas the slits 15 have their cut-outs projecting from only one of the fin surfaces.
However, as the exchange of heat is realized more actively in the first (upstream) row 12a than in the second (downstream) row 12b in all heat exchangers, the fact that there are more upstream slits 14 than downstream slits 15 means that heat transmission is realized unevenly between these upstream and downstream sides of the fin 12, resulting in a reduction in the efficiency of heat transmission.
Further, as it is common for much condensation to form on the upstream side of the fin 12, the fact that the slits 14 are formed over substantially the entire surface of the upstream side of the fin 12, means that the water generated by condensation can not easily be exhausted from the surface of the fin 12. Over time, this results in a residue forming on the surface of the fin 12 such that heat exchange efficiency is reduced.
Also, as the slits 15' formed closest to a downstream edge of the fin 12 are spaced from the pipe holes 13b of the second row 12b at a considerable distance, much air flows between the slits 15' and the pipe holes 13b.
Accordingly, air passes unevenly over the surface of the fin 12 in this area, and noise is created by the large amount of air passing between the slits and pipe holes.
Finally, as the upstream slits 14 have their cut-outs projecting from both surfaces of the fin 12, the manufacturing process is complicated and overall manufacturing costs are increased.